// flow 运行环境API(内置对象):
/**
 * @flow
 */

const element: HTMLElement | null = document.getElementById('app')



// https://github.com/facebook/flow/blob/master/lib/core.js   //js标准库定义成员
// https://github.com/facebook/flow/blob/master/lib/dom.js    //dom Api
// https://github.com/facebook/flow/blob/master/lib/bom.js    //bom  Api 
// https://github.com/facebook/flow/blob/master/lib/node.js    //node API